1. Field of the Invention
The present invention relates to a dynamic metal-oxide semiconductor (MOS) random access memory (RAM) device and, more particularly, to a system for driving a dynamic RAM device.
2. Description of the Prior Art
In recent years, dynamic MOS RAM devices have been enlarged from 16 kbits (precisely, 16,384 bits) to 64 kbits (precisely 65,536 bits). Thus, as the integration density has become high, the number of memory cells connected to one sense amplifier for the read operation has become higher and, accordingly, the load of each sense amplifer has also become higher. In order to reduce the load of each sense amplifier, for example, in a prior art 64 kbit MOS RAM device, two series of sense amplifiers are provided, and a 16 kbit memory cell array is arranged on both sides of each series of sense amplifiers. Therefore, the memory cells, sense amplifiers, row address decoders, and the like are divided into two blocks.
In a block-divided 64 K device, during the access mode, for example, for the read operation, one row is selected from each block by using row address signals A.sub.0, A.sub.0, A.sub.1, A.sub.1, . . . , A.sub.6, and A.sub.6, that is, two rows are selected. In addition, one of the two rows is selected in an output portion by using row address signals A.sub.7 and A.sub.7. Simultaneously, one column is selected from the memory cells by using a set of column address signals A.sub.0, A.sub.0, A.sub.1, A.sub.1, . . . , A.sub.7 and A.sub.7 which multiplex the row address signals.
On the other hand, during the refresh mode, which is indispensible for a dynamic device, the selection of columns is unnecessary, and, accordingly, the above-mentioned selection carried out by the row address signals A.sub.7 and A.sub.7 and by the column address signals A.sub.0, A.sub.0, A.sub.1, A.sub.1, . . . , A.sub.7 and A.sub.7 is not performed.
In the above-mentioned prior art device, however, since all of a plurality of blocks, which is for example, two blocks, is selected to operate when a row is selected during the access mode, the power dissipation of the device is large.